Recently, ammonia borane (NH3BH3, hereinafter referred to as “AB”) has been paid much attention due to its high stoichiometric hydrogen content (19.6 wt %) to meet the need of “hydrogen economy”. Dehydrogenation of AB is a three steps reaction, giving one equivalent H2 at each step. In the first step, polymeric aminoborane ([NH2BH2]n) as the main product is obtained with one equivalent H2 released around 110° C.[1].
      n    ⁢                  ⁢    N    ⁢                  ⁢          H      3        ⁢    B    ⁢                  ⁢          H      3        ⁢      →    catalysts    ⁢                    [                  N          ⁢                                          ⁢                      H            2                    ⁢          B          ⁢                                          ⁢                      H            2                          ]            n        +          n      ⁢                          ⁢              H        2            
However, the polymeric aminoborane, which was generally described as polyaminoborane (hereinafter referred to as “PAB”), is actually a mixture of amorphous linear, branched and cyclic oligomers and polymers. At the same time, researchers used transition metal, acid, base and ionic liquid to catalyze dehydrogenation of AB in solution[2-5]. But the crystallinity of products was either amorphous or not mentioned. Heinekey et al. catalyzed dehydrogenation of AB by using (POCOP)Ir(H)2 in THF solution to obtain cyclic pentamer (NH2BH2)5[6]. However, the catalyst (POCOP)Ir(H)2 is a complex metal organic compound which is not convenient to get. No other reports were published about the formation of crystalline PAB from the dehydrogenation of AB.
As derivatives of AB, metal amidoboranes and amine boranes can also dehydrogenate under certain condition or on catalysts. However, no reports were published about the crystallinity of the post-dehydrogenated products through solid reaction.